Apparatus for forming cutting elements



Sept 24, 1963 T. H. sHEEHAN APPARATUS FOR FORMING CUTTING ELEMENTS 5Sheets-Shea?I l Filed Aug. 4, 1960 2 27( INVENTOR:

Sept. 24, 1963 T. H. sHEEHAN 3,104,500

APPARATUS TOR FoRMING CUTTING ELEMENTS Filed Aug. 4, 1960 5 Sheets-Sheet2 Sept- 24, 1963 T. H. sHEEHAN 3,104,500

APPARATUS FOR FORMING CUTTING ELEMENTS Filed Aug. 4, 1960 5Sheets-"Sheet 5 75H5 INVENTOR.

Sept 24 1963 T. H. sHEEHAN 3,104,500

APPARATUS FOR FORMING CUTTING ELEMENTS Filed Aug. 4, 1960 5 Sheets-Sheet4 IN V EN TOR.

Sept. 24, 1963 T. H. SHEEHAN 3,104,500

APPARATUS FOR FORMING CUTTING ELEMENTS Filed Aug. 4, 1960 5 Sheets-Sheet5 E x Y,

0 i5 6,1 INKENTOR.

United States Patent O 3,104,500 APPARATUS FR FOG CUTTING ELEMENTSThomas H. Sheehan, Chicago, lli., assigner to Sunbeam Corporation,Chicago, Ill., a corporation of Illinois Filed Aug. 4, 1960, Ser. No.47,536 5 Claims. (Cl. 51-89) This invention relates to an improvedapparatus for forming cutting elements land, more particularly, to animproved apparatus `for forming undercut teeth on shear cutting tools.

The -invention will `be described in detail in `connection with themovable cutting element of a reciprocating type of electric dry shaver.However, such description of my invention is only illustrative of myinventive teachings and is not to be taken as being limiting.

In one well known form of reciprocating type of electric dry shaver Ithemovable cutting element comprises a generally channel-shaped elongatedmember. Shearing teeth are integrally defined on the bight portion ofthe channel-shaped member by slots which extend across said lbightportion. It would be desirable to provide said shearing teeth with anundercut. An undercut is advantageous since it provides the teeth withsharp edges which are more eiicient and provide a more comfortableshave.

In this type of cutting element undercut shearing teeth and theiradvantages are well known to those skilled in the art. Nevertheless,until my invention the methods and apparatus Afor forming said undercutteeth have not provided teeth with hard, sharp edges, and said methodsand `apparatus also have not been quick, uncomplicated, low cost andefficient.

For instance, `one prior art method may comprise rst punching openingsin hat stock and then coining or swaging the `openings to provide anundercut and then lapping the stock to make the edges of the openingssharp. This does not always result in undercut shearing edges which havea high' degree of sharpness or provide a comfortable shave. It will beappreciated that a high degree of sharpness is desirable since thisreduces the shaving time required and contributes to shaving comfortsince with efficient and sharp edges there is no hair pulling or thelike. Quick shaving is advantageous since the shaver can be operated atslightly higher speeds without danger of overheating due to reducedtotal shaving time. Shaving comfort obviously is a very importantconsideration, and particularly in the case of the shaving of facialhairs or whiskers. v

After the prior art method step outlined above it is customary to thenform the flat stock into the required channel shape. The subsequentforming `operation may introduce undesirable deformations or strains inthe teeth of the stock. After the Iforming operati-on, the stock is thenheat treated in an inert atmosphere and quenched. The stock isconventionally a carbon steel and if the heat treating atmosphere isntcarefully controlled, there may be some de-carb-urization of the teethedges. This means that the teeth edges will not have the required degreeof high hardness. Therefore, it would be desirable to form the teethafter the stock is fabricated into channel shape and heat treated andquenched. This way there will be no deformations or strains introducedinto the "ice teeth since there will be no bending thereof subsequent totheir formation. Also, if there is any de-carburization during heattreating the soft outer surface of the stock will be removed -by thesubsequent teeth for-ming operations which will leave only teeth edgeswith the required degree of hardness. Y

Furthermore, itwill @he obvious `fro-rn the above outlined prior artmethod that several separate vand distinct opera-tions are requiredwhich do not result in teeth edges which are sharp. These steps arepunching, coining or swaging and lapping. It would be an advantage toreduce the number of operations required. y

Accordingly, it is an object of this invention to provide an improvedapparatus for forming improved undercut teeth `on a shearing tool. n

It .is a further object of this invention to provide an improvedapparatus for forming improved undercut teeth on a shearing tool whichwill overcome the disadvantages mentioned heretofore -in prior artmethods and appara-tus andtheir products.

A further object of the invention is to provide an improved apparatusfor :forming improved undercut teeth on the generally U-shaped shearcutting elements of electric dry shavers. Y

In my invention a grinding 'operation is used in forming the undercutteeth. This grinding operation takes the place of the heretoforementioned punching and coining or swaging steps. Ilhe lgrindingoperation forms sharper edges than heretofore obtained with punchingandY coining or swaging. Furthermore, the grinding operation =followsthe channel lforming and heat treating operation. Therefore, harderandmore deformation and strain `free `sharp edges are attained yon theshearing teeth than attained with prior art procedures, although it ispossible to use my teachings to advantage by grinding before channelforming and heat treating.

` -In the invention lthe grinding is preferably performed with a pluraldisc cone-shaped grinding wheel, and opposite sides of the undercutteeth are formed essentially by mere relative reversal between the`stock and wheel. This contributes to manufacturing methods andapparatus which are'quick, uncomplicated, low cost and efficient.

The features of my invention which1 I believe to be novel are set forthwith particularity in the appended claims. The invention itself,however, bothY as to its organization and method of operation, togetherwith further objects Iand advantages thereof, may best be understood byreference to the following description taken in connection with theaccompanying drawings.

In the drawings,

FIG. 1 is a perspective view of a shearing tool formed by my invention;

FIG. 2 is a diagrammatic illustration of the 4relative positioning ofthe shearing tool and grinding wheel during the iirst pass of theseparts relative to each other;

FIG. 3 `is an illustration similar to FIG. 2 during the second pass;

FIG. 4 isla top view of the shearing tool after the rst pass;

FIG. 5 is a top view of the shearing tool after the second pass;

FIG. 6 is -a top view of one form of apparatus of my invention;

FIG. 7 is a front View of the apparatus;

FIG. 8 is a side view from :along the line 8 8 of FIG. 7;

FIG. 9 lis a sectional view taken along the line 9 9 of FIG. 6;

FIG. 10 is a sectional view taken along the line itl-1l) of FIG. 7;

FIG. l1 is a sectional view taken along the line 11-11 of FIG. 10;

FIG. 12 is a sectional view taken along the line 12-12 of FIG. l; and

FIG. 13 is a sectional view taken along fthe line 13-13 of FIG. l0.

Referring now to FIG. `1 of the drawings, illustrated 'therein is ashear cutting tool 1 which is intended .to be used with an electric dryshaver. This cutting tool is Vexemplary of shearing instruments whichcan be manufactured by my invention. The panticular type of shearcutting tool illustrated in the drawings is intended to 'be used with anelectric dry shaver ofthe type disclosed in co-pending Ivar Jepsonpatent application Serial No. 848,102 led on October 22, 1959, for anElectric Dry Shaver, and which is assigned to the same assignee `as :theinstant patent application.

Although the shearing tool illustrated in the drawings nis intended tobe reciprocated back .and forth in a lengthwise direction with relationto a not shown cooperating outer slotted or apertured stationary comb,it will be appreciated by those skilled in the art that the inventionkis not restricted to movable shearing tools.

The cutting -tool 1 comprises an elongated member which is generally Uor channel-shaped in transverse cross section. That is to say, thecutting -tool comprises a pair of sides 2 andan inter-connecting bridgeor bight por-tion 3. This U or channelshape. is fabricated from carbonsteel stock. A pair of cross pieces 4 are connected to the opposite ends.thereof such as by @et Welding or the like. After the shearing teeth 5are 'formed on the bridge or bight portion and other finishingoperations 'are performed on the element, a spring member 6 is connectedto the .two cross pieces. The central portion of the spring iscorrugated and it is adapted to receive one end of a not-shown operatingar-m .or lever which is driven by the shaver motor so as to reciprocatethe cutting element in a lengthwise direction. lThis spring provides aresilient connection between .the cutting element and the operating arm.

The bridge or bight portion has fa lengthwise extending centraldepression 7 formed therein to in effect define two U of channel-shapedparts in the bridge or bight portion. The teeth which are formed on fthetwo U or channel-shaped parts of the bridge or bight portion are alignedwith each other and the central depressed portion serves as -astrengthening portion. The teeth are formed on the outside of the bridgeor bight pontion and their opposite sides 8 yand 9 are undercut asillustrated in FIGS. 2 and 3. That is to say, the corners 10 and 1.1(sce FIGS. 4 and 5) of the teeth are the shear cutting edges thereof,and the opposite sides of the teeth con-verge towards each other whenviewed from the inside of Vthe element. The undercut sides of the teethyare inclined at an angle of about eleven rdegrees with respect to thevertical axis of the teeth inasmuch as this angle of inclination hasgiven excellent results. However, (the invention is not necessarilyrestricted to lan angle of Iabout eleven degrees.

The teeth preferably extend angular-ly across the bridge or bightportion. That is to say, the teeth are inclined at an angle of abouteleven degrees with respect to a transverseY perpendicular plane:through the bridge or bight port-ion. This particular angle has 'beenselected inasmuch .as it provides excellent results. However, theinvention is not necessarily restricted to this'angle, and the teachingsof the invention can also be used to advantage in a shearing elementwhich does not have its teeth extend angularly across the same. f

grinding edges on the grinding discs.

The teeth are formed on the channel or U-shaped inember after it :isbent into the required configuration and given a heat treating andquenching operation. The teeth are formed in the member by a grindingmethod and apparatus. teeth are ground in the element, the outer surfaceof the bridge or ibight portion is lapped .to give the corners 10V and11 a very high degree of sharpness yand to remove any bur-rs which mayhave Ibeen formed thereon during the grinding oper-ation. The shearingelement is finished by electro-etching the same and giving it a hardchromel iinish. The electro-etching is for the purpose lof removing anyburrs which may be present and which were not removed by the lappingoperation. Such burrs may present at the corners of the teeth adjacentto the sides of the U -shaped element.

Referring now to FIGS. 6 to 13 of the drawings, illustrate-d therein isan apparatus which comprises a table 15 which has a rotary carriage 16and a pair of rotary spindles 17 and a pair of grinding wheel dressingmeans K 1S mounted thereon. The carriage is generally circular inoutline` and is vertically disposed with its shaft 19 being mounted forrotation in a bearing housing 20. The

bearing housing is mounted yon the table on a frame 21.

The shaft 19 of lthe carriage is driven by 'a motor 22 through la gearreduction mechanism 23 and a pulley belt arrangement 24 which isconventional.

Each of the spindles 17 lhas an arbor 2S mounted thereon which carries agrinding Wheel 26 which has .the form of a truncated cone. The grinding-wheels 26 are bui-ltV up out of a .plurality of Iaxially yaligned andspaced grinding discs '27. The grinding `Iwheels are positioned on vdia'metrically opposite sides of the carriage. The 'area adjacent thetop of the Icarriage land between the twoV grinding wheels is a loadingand unloading station for the stock which is rto be ground *by thegrinding wheels.

Of course, it will be appreciated that the two grinding Each of :thevspindles has motor means 30 for rotating the same independent ofrotation of the carriage. Such independent drive means for the spindleis desirable for the purpose of dressing the grinding wheels. Thedressing `means which comprises a diamond -tip 31 is located adjacent toand outboard of the grinding wheels. 'Ihe dressing means 18 is manuallyoperative for moving the diamond tipped dressing tool along the lengthof Ithe grinding wheel and in parallel relationship tothe cone-shapedperipheral surface of the grinding wheels. When the diamond .tippeddressing tool is moved along the grinding wheels the .grinding wheelsare rotated by the independent drive means 30 dior the spindles and inthis manner the grinding Wheels are dressed so as to maintain the sharpThe cutting elements are mounted on the carriage so as to be moved pastthe grinding 'wheels as the carriage rotates counterclookwise whenviewing FIG. 7 although` grees since it is desired to have the teethextend angularly f acnossrthe cutting `elements at this angle., ILE theelements were parallel .to .the axis of the carriage, the (teeth wouldextend perpendioularly across the cutting elements Y in view of the4disclosed disposition of the 'grinding Wheels with respect to thecarriage axis.VV Itis possible to have the cutting elements disposedparallel to the carriage axis After the undercut and angularly disposedFun and to provide for this Aangular disposition ott the teeth by properpositioning of the grinding wheels and lengthwise movement of thegrinding Wheels and elements with respect to each other during grinding.However, it is preferred to provide sfor lthis angular disposition ofthe teeth by inclining the cutting elements with respect to the carriageaxis since this arrangement is mechanically much less complicated.

For instance, the spindle axes are parallel to each other and they aredisposed in a plane which is common to these axes and the axis of thecarriage. The spindle axes are inclined within :this plane at -an angleof about 11 degrees relative to the carriage axis to provide the l1degree undercut sides yof the teeth. if the cutting elements were notinclined |to the axis oi the carriage then it Iwould be necessary totilt the spindle axes out of this plane by ll degrees in order to havethe teeth extend angularly by lil ydegrees across lthe cutting elements.Also, it would be necessary to move the grinding wheels or elementslengthwise as they pass under the grinding wheels.

As heretofore noted, it is within the scope orf the invention toposition the Lgrinding wheels other than on diametrically Opposite sidesof the carriage. In such situation the ,grinding wheel axes would not beparallel to each other and disposed in a common plane with the carriageaxis. Nevertheless, for the plane which was common to each grindingwheel axis and :the carriage axis each grinding wheel axis would stillbe inclined lonly within its corresponding plane provided the cuttingelements were angularly disposed on fthe carriage. Oi course, thespindle axes would not be parallel to each other.

Since the grinding wheel axes are inclined to the carriage axis at anangle of ll degrees this means that the grinding discs 27 are inclinedwith respect to the cutting elements at an angle of 79 degrees. It isthis 79 degree inclination oi the grinding discs whioh accounts ci the1l degree undercut sides ott the shearing teeth. Since the grindingWheels grind the Iopposite undercut sides of the teeth the grinding.wheels are reversed with respect to each other. That is, one grindingwheel has its narrow end directed toward one end of the cutting elementsand the other grinding wheel is pointed in the opposite direction.Another way of looking at it to say that the discs of one wheel areinclined toward one end of the cutting element and the discs of theother wheel are inclined .toward Ithe other end. In other words, thewheels 26 have been reversed with respect to each other so that theywill :form opposite undercut sides oi the teeth. it will be :obvious ltothose skilled in the art that opposite sides of the teeth could beformed by a single grinding wheel by reversing the single lwheel and thecutting elements with respect to each other end for end when grindingopposite sides with the same single wheel. However, two end ttor endreversed grinding wheels are preferred since this is a much simplerarrangement.

Since the grinding Wheels are located on diametrically opposite sides ofthe carriage their discs are parallel to each other. This would not betrue if they Werent so located. in any event, the discs of the end dorend reversed wheels are positioned with respect to each other so thatthe discs of one wheel will enter the cutting elements at substantiallythe same points as in the case of the other wheel although in adifferent direction of inclination but at the same angle of 79 degrees.This is illustrated diagranunatically in FIGS. 2 and 3. FIG. 2corresponds to a top view of the cutting element as it passes under theleft hand Wheel 26, and FIG. 3 as it passes under the other grindingwheel. A slight clearance l2 is provided between rthe right handgrinding wheel and the undercut sides 3 formed during the rst pass sothat these sides and their corners lll `are not destroyed during thesecond pass.

Gne reason for using cone-shaped grinding wheels is to obtain a largenumber 4of undercut teeth which are identical fto each other and have arelatively low height. Obviously, cylindrical shaped grinding wheelshaving a plurality of spaced grinding discs which are disposed at anangle similar to the cone-shaped wheels could be used to provideundercut teeth. However, the teeth would not be identical but irregularand some or them would have to be quite deep if a relatively langenumber or them were going to be formed.

The apex of the cone-shape for each wheel 26 has an angle of 22 degrees.That is to say, the sides of the coneshapled wheels are .sloped at anangle yof l1 degrees with respect to their axes. Since these axes aretilted 11 degrees with respect rto the carriage axis, all the discs 27orf each wheel will simultaneously enter the cutting elements. rllhismeans that all the ground teeth will be identical to each other and alange number of them can be formed with relatively shallow ground slots.

In the practice of my invention, it is not absolutely necessary that thecarriage be circular. Ilfior instance, the carriage could comprisemovable iixture means which did not move in a continuous closed cycle.The disadvantage of such an arrangement is that the movable hxture meanswould have [to be reversed periodically. 'Ilhereore, preferably theinvention is practiced .with a carriage or conveyor means which willmove the elements continuously in a closed cycle. Additionally, it willbe obvious to those skilled in `the art that the carriage need not bethe movable part of the apparatus, but the carriage could be fixed andthe grinding wheels could be caused to move about the carriage. However,the disclosed arrangement is preferred due to its inherent simplicity.Furthermore, although the inventionhas been explained with respect Itoteeth which have and 11 degree undercut and an ll degree angulardisposition, the angle of the undercut can be different firom theangular disposition ci the teeth across the cutting-element.

Phe means for mounting the cutting elements on the carriage 16 and theloading and unloading means will now be described. The carriage 16 ispositioned between a pair of cam plates 35. As the carriage rotatesbetween the cam plates, roller cams 35 of the carriage ride on the camplates .for automatically controlling the holding and releasing positionof the means rfor mounting the cutting elements fon the periphery of thecarriage. In particular, a plurality of spaced mounting elements 37 are-angularly disposed along the circumference of the carriage. Fllhecutting elements l are inserted between each adjacent pair of mountingelements 37. A pressure plate or pad 38 underlies each cutting elementand reach pressure pad 38 is urged in an upward 1direction by a springbiased plunger 39. rPhe plunger is movable within a cylinder l0 and aspring 41 is inserted inside the cylinder for spring biasing the plungerin an upward direction. The pressure pad 38, spring biased plunger 39and cylinder dit can be moved in an outward direction by a pin 42 or thelike which underlies the cylinder. The pin is disposed parallel to theaxis of the carriage and is movable within a slot 43 formed in thecarriage. The rollers 36 are mounted on opposite ends of the pin andpositioned so as to ride on the cam plates 35. When the rollers ridealong the curved portion 35 of the cam plates, the pin -is movedradially outward yand the same applies for the cylinder, spring biasedplunger and pressure pad. This causes retention of the cutting elementsin the space dened between adjacent pairs otf mounting elements 37 andthe pressure pads 33 by spring pressure. However, when the rollers leavethe curved surfaces of the cam plates the cylinder 40 is no longer urgedin a radially outward direction but is free to tall radially inward.This relieves the resilient spring pressure on the pressure pad so thatflihe cutting elements can be readily removed. The non-curved portionor" the cam plates is indicated by referencey numeral d 35 and ispositioned in the loading and unloading area 7 of the apparatus locatedat the top thereof between the grinding Wheels.

The elements 1 are retained between the mounting members 37 by tabs 50`or the like formed at opposite ends and sides thereof. When the springpressure on the elements 1 is relieved they can be 'withdrawn [trom inbetween members 37 by sliding them out. The part 16 is an integralextension of carriage 16. At its outer periphery part 16Vhas a pluralityof axially extending spaced slots 51 formed therein. These slots 51receive lugs 52 Vor the like formed ion the bottom yof members 37 riorproperly aligning the same. The lugs 52 are disposed at an angle of l1degrees with respect to the lengthwise axis of members 37 so that thelatter will be disposed at an angle of ll degrees with respect to theaxis of the carriage 16. The members 37 are retained in their slots S1by studs 53 or the like extending through members 37 into part 16. Sincethe slots 51 extend parallel to the axis of carriage 16 if it is desiredto change the angular disposition of the teeth on the elements 1 thiscan be readily accomplished by using other members such as 37 which hauethe desired angular diiference between their lugs 52 and lengthwiseaxis.

The pressure pla-te or pad 38 is not Adirectly engaged by the plunger 39but through the intermediary oi a pressure block 54. The pressure plate38 has a swivel connection with the block 54 by virtue of a transversecurved lug 55 formed on the bottom of pad 38 which is received in asimilarly curved transverse slot d iormed in the upper part of blocks5d. Thus the plates or pads 3S can rock slightly about their centralportions.

rIihe assembly of the pads 33 and blocks 54 is retained on the carriageby :tabs 57 or the like formed on opposite ends 4oi blocks 54 whichextend into grooves 58 4formed in a pair of annular side carriage plates59. Plates 59 are retained on carriage 16 by studs 6) or the like. Theblocks S4 are received in suitable slots 61 `formed in the outerperiphery of carriage part 1d between the slots 51. The cylinders 49 andtheir plungers are positioned within suitable radially extending bores62 formed in carriage part 16' and the slots d3 extend through the sideplates 59 as lwell as the carriage part 16'. The pins 42 are retained inIthe slot 43 by washers 63 or the like interposed between the ends ofpins 42 and rollers 36.

Front and `rear cam mounting plates 'Til and 71, respectively, aresupported (from the bearing support frame 21 by studs 72 or the like onopposite sides oi the carriage 15. These mounting plates 7i) and 71support cam plates 35 by means such as not shown studs or the like.Supported on the top of bearing housing 2d is a mounting plate 73 whichhas a plate 74 supported therefrom. 'lille plates 7i) and 71 supportlower oil and air pressure defliverers 75 and the plates 73 and 74support upper oil and air pressure :deliverers 76. The deliverers 75 and76 deed atomized oil and air pressure to the work 1 as it passes beneaththe grinding wheels 26 for cooling the work 1 and Wheels 26 during `theteeth grinding operation. The upper deliverers 76 are branched orY-shaped so as to deliver atomized oil and air pressure to the grindingwheels 26 as Well as the work V1. Cooling of both the grinding wheelsand the cutting elements 1 is necessary since the grinding wheels arehigh speed rubber or lthe like abrasive wheels. The high speeds andabrasive friction between the work 1 and discs 27 results in thegeneration fof large quantities of heat. Ii sufficient cooling Wasnltprovided the discs would become overheated and scorched and Wearquickly. Aside iirom desiring to perform the grinding operation quickly,high speeds are necesasry since the rubber or the like abrasive discsare not rigid, but thin and flexible. However, when they are rotated ata high speed centrifugal force in efrfect makes them act as stiffgrinding discs which quickly and accurately grind their way into thesteel stock. In one form of the invention the fdiscs 27 had a fthinnessand spacing on Ithe order of twenty-tive thousandths of an inch. Theywere hard but ilexihle enough to be bent with finger pressure. However,using rubberized or the Rike abrasive wheels means that they can bereadily cforrned to the required thinness as contrasted with other typesof grinding sdiscs. Also, while they are rotating at a lhigh speed theywill operate similar to grinding discs constructed from rigid materialsbut will not have their disadvantage :of britrtleness or being apt tocrack or become chipped. -One form of abrasive rubber grinding discwhich has provided excellent results is identied by` the designation 120POR, manufactured by fthe Norton Company or Springliefld, Massachusetts.

The dressing means are supported adjacent the wheels 26 on support posts77. The adjusting means 29 can be used to adjust the depth of out madeby the discs 27V of the Wheels 26. The manual adjusting means 28,` 2,9is conventional and is for the purpose of moving the spindles lengthwiseor sidewise on guideways such as 78 as will be readily understood bythose skilled in the art.

The apparatus is not limited to forming undercuts of l1 degrees inasmuchas the spindles 17 can have other shaped grinding wheels mounted thereonand the angle between the spindles 17 and the axis of the carriage canbe adjusted. The adjusting means for changing the angle between thespindles and carriage axis may comprise a not shown indexed rotatablemounting of the spindle motor housing 30 on its support platform 79, asis well known in the art and diagrammatically illustrated in FIG. 6 by-brokendine circles in the area of parts 30 and 79. Thus, by changing.the angle of the spindles 17 and using diierently cone-shaped grindingwheels, a wide range of different angles of undercut teeth can fbeobtained.

While there has heen shown and described a particular embodiment of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention, andthat it is intended by the appended claims to cover all such changes andmodiiications as come within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. An apparatus lfor forming undercut teeth across metallic shearcutting elements of electric dry Shavers, said apparatus comprising arotatable, circular and vertically disposed carriage, a rotatable,truncated coneshaped 4grinding wheel being provided along diametricallyopposite lateral sides of said carriage, the axes of said carriage andgrin-ding wheels being disposed in a common horizontal plane, eachygrinding Wheel comprising a plurality of thin and ilexible grindingdiscs, said rdiscs being composed `of rubber and abrasive material, saiddiscs being parallel and closely spaced with respect to each other,means for rotating said grinding wheels at high speed to imp-artrigidity to their discs by centrifugal lforce,- mounting means on saidcarriage adapted to receive said cutting elements, means for-automatically releasing said mounting means along the upper part ofsaid carriage, and said grinding wheels being reversed with respect toeach other -to grind opposite sides of said undercut teeth.

y2. In an apparatus as in claim 1, means for lfeeding a fluid coolingmedium to both said cutting elements and said Igrinding wheels, and saiddiscs having a thinness and Y spacing of the order of twenty-livethousandths of anv discs composed of rubber and abrasive material, saiddiscs iii;

being parallel and closely spaced with respect to each other, means for`rotating said Wheel at high speed to impart rigidity to said discs bycentrifugal force, and means for simultaneously engaging the edges ofeach of said discs with one of said cutting elements.

5. In an apparatus as in claim 4, including means for feeding a fluidcooling medium to both said cutting elcment and grinding wheel, and saiddiscs having a thinness and spacing of `the order of twenty-fivethousandths of an inch.

References Cited in the le of this patent UNITED STATES PATENTS HullFeb. 28, Krug M-ay 18, Hawn Mar. 26, Cummings Apr. 12, Schick May 11,Schweiker Dec. 19, Martin Nov. 5, Russell May 16, Noxley July 15,Trottier Nov. 19,

Mader et al.l July 26,

1. AN APPARATUS FOR FORMING UNDERCUT TEETH ACROSS METALLIC SHEAR CUTTINGELEMENTS OF ELECTRIC DRY SHAVERS, SAID APPARATUS COMPRISING A ROTATABLE,CIRCULAR AND VERTICALLY DISPOSED CARRIAGE, A ROTATABLE, TRUNCATEDCONESHAPED GRINDING WHEEL BEING PROVIDED ALONG DIAMETRICALLY OPPOSITELATERAL SIDES OF SAID CARRIAGE, THE AXES OF SAID CARRIAGE AND GRINDINGWHEELS BEING DISPOSED IN A COMMON HORIZONTAL PLANE, EACH GRINDING WHEELCOMPRISING A PLURALITY OF THIN AND FLEXIBLE GRINDING DISCS, SAID DISCSBEING COMPOSED OF RUBBER AND ABRASIVE MATERIAL, SAID DISCS BEINGPARALLEL AND CLOSELY SPACED WITH RESPECT TO EACH OTHER, MEANS FORROTATING SAID GRINDING WHEELS AT HIGH SPEED TO IMPART RIGIDITY TO THEIRDISCS BY CENTRIFUGAL FORCE, MOUNTING MEANS ON SAID CARRIAGE ADAPTED TORECEIVE SAID CUTTING ELEMENTS, MEANS FOR AUTOMATICALLY RELEASING SAIDMOUNTING MEANS ALONG THE UPPER PART OF SAID CARRIAGE, AND SAID GRINDINGWHEELS BEING REVERSED WITH RESPECT TO EACH OTHER TO GRIND OPPOSITE SIDESOF SAID UNDERCUT TEETH.